Dynatron oscillator



Aug. 13, 1935.

DYNATRON OSC ILLATOR Filed June 15, 1952 2 Sheets-Sheet 2 0 W4 lmlmmlm l 6' 50' lwmlmmmlmh 3mm:

P. o. FARNHAM 2,011,290

rangements that are" welladapted for tuned" and/or for modulated dynatron oscillators; ,The-magnitudeiof the output voltageof "a; dynatron oscillator, -for 'constantcontrol: grid' bias; will vary" withitl'ie'load impedance and; in o'scill-at'ors' all frequencies:

Patented Aug; 13, 1935 mesne Iassig nments, -cto Badior Corporation of Amenica,, New York N. Y., a' tcorporation of Delaware;

Application? June I5; 1932; Serial 'No: 6'1 m4 46 This invention 'relates to L dynatron' oscillators and particularly "to; methods of and circuit" ar having a plate? circuit" tunable over aifre'quency band; the output is"usua1lyfar 'fr'oml constant at' by a lowfrequency voltage impresseu in the com trol-grid circuit, the percentage 'of h'armoriics present inthe output circuitof th'e'known dyn'atron i oscillators" varies materially with: thetuning; .15

Objects: of this invention are to provide met'l'i OGSiOf andtcircuiti arrangements forniaintaining the output voltage: of a' dynatronl oscillator subv stantially independent' for Wldevarlations of the plate load impedancega-nd fonreducing thefpro 20 duction of harmonic frequencies i'n modulatedi cl ynatron oscillators.- 1 Further objects are to. pro-- 1 VldQ lTlQlbhQdS Of andcircuit anangements' for automatically varyingthe controlv grid} biasof a tuneddynatron oscillator asa: function of th'eam t plitude of oscillation and; at suchl rateas'to pro-rvide a predeterminedirelation'between the output voltage and the oscillating frequency; "More specif cally an object is'toprovidea, tuned idyhatron oscillator circuit incl-uding a rectifierfor automaticallilr, developing a direct currentgridabias poteritial'byrectification of theos cillatory voltagedeveloped in theoutputcircuit of'the oscillator! r specification in which:

These and other objects andladvantagesofthe mventiomwill' be apparent fromfthe following Fig; 1 isa curve sheetshov vi ng the relationship between the dynatron output voltage andcontrolm impedance; a a Figs. 2, 3, 4 andbare circuitdiagramsof dynatron oscillators embodyingtheinvention.

Inthe curve'isheetJFig. 1', the curves ALTB and grid bias for different? values of the lplate lbaui will be recognized as typical curves illustrating the a relationship between the pealr' oscillating voltage ofia dyna'tron and the direct current control grid A bias, the several curves being obtained for differ-T ent values-of the plate load impedance, Ralof' the OSCillttOlf. The tuned." circuit ofialfi I oscillatbp de signedfibrjopjeration ovejr 'afrfequency and is" usually the plate impedance and, in'the case of the usual tuned circuit, the impedanceof this load varies with the tuning. In Fig. 1f, the three curves represent the voltage-grid bias" relationship for different frequencies' 'ii e., cur ve A"corresponds-toa lbw frequency or' relatively low lo'ad impedance;

When the? output is modulated moi-aims. (01.250 36) 1 r p curve B' corresponiis to a higher frequency or'a higheribau'impedanee; while c'urveC correspondsto a lii gh freque'ncvor'relatively'liigh"loaddinpedf According: to the known methods or operating the dynatron-"o'scillat'or a: fixed negative bias has been provided by a cathoderesistoror" by a separate" sourceof bias voltage; With' a; cathode re sister, the direct" current bia's'on the"g ri'd does not vary'jwitn tlieoutput v'o'ltagebutis dependent only upon th'e 'plat'e" and screen grid potentia'lsi- For a fixed negative bias of the value iiidi'catetl byO Ff the operating pointP' would'hef favora'fily located'whenthe cirouit*is tuneuito" the frequency corresponding to curve B: A'sthe" oscillator? is"- a'ti'n'gpoint wiu not'be 1o'cate d atthecenter of theapproxlniately linear ortion of the 'cl'i'ara'cteristioeurve; the higher frequencypf' curve A;

the-operating" pointPi wi11 "fall on thelowerourveu' section of the characteristic, and for the lower frhuencyycurvec; theoper'atin'g ppintPi wilrfall at theupper-oend of the curve These curves therefore: explain" the difli'cultieswiiionhave Been experienced in designihgdyhatron oscillators *f 0'! operation overabamm frequen ies, since a fixed bias tha'tis appropriate for a -high voltageoutput at" one frequency will result in a lowered output forotherfrequencies. v v

In accordance with the present invention, the

' con'trblgridbias isautbmatiealiy varieda's'a time; tion of' the output voltage, the change inbias voltagef-bem'gin such sense and atsucfi a rate as? voltage.--

As shown' in Fig; 2, the dynatro'n oscillator iiicludesai tetrode I havinga tuned plate circuit; L0 and the" voltages impressed upon the 'plate (P and to maintain-an; approximately onstan't output screengrid G'z from thesourc'es indicated by E15 and E15; respectiveIy, are such that the tube has a negative pla'te' resistance. The control" grid Gr is connected to the cathode through a resistance R whichus Icy-passed by'a conuenser Ci. resistance R for rns the output circuit of a-Tdiode-rectifier fiwhich has; an input circuit comprisingi'an' inductance-L1 that is coupled to the? plate" inductance L. I It will: be apparent that the oscillatingvoltage E of the tuned plate circuit LC establishes avolt'- age E1: across: theinductancelli and: that; due to the dio'de rectifieraction; a direct current voltage is": developed acros'sl th'e resistance R. The: bias voltage across the resistor" R varies as a substan ti'allyi linear: function of the peak oscillating volta'g E and-is repzeserit'ed in Fig. 1 by the straight line 01), the slope of the line OD being approxilocation of the battery 4' provides the desired mately unity, using the scale of oscillator voltage marked E2.

The voltage ratio, E2/E, may be so chosen that the operating point P falls at the center of the linear portion of curve B, as in the case of a fixed bias OF. If'the circuit shown in Fig. 1 is tuned to other'frequencies, the operating point will not move along the ordinate PF, as in the prior cir-" cuits employing a fixed bias, but will move along the line OD. The variation of output voltage with tuning is therefore much less than that which was observed with the known oscillator circuits.

The control grid bias voltage of the Fig. 2 circuit falls to zero when the tube is not oscillating since the bias voltage is derived solely from rectification of a voltage developed in the output circuit. As shown in Fig. 3, a fixed bias voltage Ec may be impressed on the grid to insure a substantially negative bias over the entire operating range of the oscillator. This bias may be provided by a battery or other current source 3 which is so connected between the grid G1 and the resistance Rthat a positive bias is impressed on the grid when the output voltage E falls to zero. Toobtainrelatively large changes in the current flow through rectifier 2 for small changes in the value of the output voltage E, the inductances L1 may includea larger number of turns than the j plate inductance L. The voltage E2 on the rectifier-may thus be made much greater than the v voltage E.

, a diiTerent scale for the ordinate E2 and is drawn through the zero ordinate at a point representing,

on'the same voltage scaleas the voltage E2, thefixed bias Ec. By appropriate choice of the stepup ratio of the transformer L, L1, and the bias Ec,

, this linewill intersect, the curve B at the desired operating point P. With the Fig. 3 circuit, the operating point P will move along the line HI when the oscillator is tuned over its frequency band. It will be-noted that such operation is to be preferred to that of the Fig. 2 circuit, since the line H passes approximately through the centers of the linear sections of the several curves. Another circuit for holding the locus of the operating point P to a line such as the line HI is shown in Fig. 4, in which the rectifier circuit includes a source of bias voltage, such as a battery 4, for impressing a negative potential on the rectifier plate P1. The diode will not pass a rectified current until the peak voltage E2 exceeds thedelay action bias voltage EK that is introduced by the battery 4. The effect of this delay ,action is to reduce the control grid bias to zero when the peak voltage E2 on the rectifier decreases to and below t -ae valued: the diode bias voltage Ex. In Fig. l, the line OII-I indicates the relationship between the control grid bias and the peak oscillating voltages-E, E2; 7

An examinationof Figs. 2 and 3 will show that the cathodes of the dynatron and of the rectifier are at the same potential. It is therefore possible to combine these two tubes in a single envelope. Such an arrangement as applied to the Fig. 4 circuit is shown in the modulated oscillator circuit of Fig. 5.

In addition to the usual tetrode elements, the tube 1 includes an auxiliary plate P1 adjacent the cathode. As compared with the Fig. 4 circuit, the battery 4' for applying the delay action bias to the diode is connected between the input inductance L1 and the output resistanceR, This bias on the plate P1 but does not establish a fixed bias between the cathode and the control grid G1 of the dynatron. The secondary winding of an audio frequency transformer 5 is connected between the control grid G1 and that terminal of the resistance R, which joins the battery 4'. A microphone 6 is included in the primary circuit of the transformer 5'.

An audiofrequency by-pass condenser C2 is shunted across the battery 4' and the resistance R. In the circuits described above, the by-pass condenser may be comparatively small as its only function is to prevent the development of a signal frequency voltage across the bias resistor R.

In the modulated oscillator, however, the by-pass must have such low impedance for the modulation voltage that the direct current bias does not vary with the modulation voltage. The peaks of the modulation voltage will vary the instantaneous voltage between G1 and cathode but the large condenser C2 will render the rectifier output substantially independent of these fluctuations of the oscillating voltage.

It is possible, of course, to employ a modulation voltage Em of such magnitude that the instantaneous voltage swings'are carried to or past the bends of the characteristic curve but, in general, the modulation voltage will be of such magnitude that the operation takes place entirely upon the linear portion of the characteristic when the operating point is located approxi-- mately at the center of that linear portion.

While the described circuits indicate the general methods which are contemplated by the present invention, it will be apparent, to those familiar with the design and construction of oscillators, that the same method of operation may be obtained with other circuit arrangements. Manual controls may be provided for adjusting the magnitude of the voltage ratio E2/E or for adjusting the relatively fixed bias voltages, thus providing for flexibility in the control or adjustment of the oscillator. The rectifier output may, if desired, be amplified to increase the sensitivity of the bias variationwith changes in the amplitude of the oscillating voltage.

These and other changes which may bemade inthe choice and the relationships of the circuit elements fall within the spirit of my invention as set forth in the following claims.

I claim:

1. In the operation of a dynatron oscillator havinga cathode, a control grid and at least two other electrodes; a tuned circuit connected between one of said other electrodes and the cathode; and means impressing on said other electrodes steady potentials which are both positive with respect to the cathode and of relative values resulting in the production of dynatron oscillations; the process which comprises rectifying a component of the oscillatory current to obtain a direct current voltage that varies with the oscillating voltage, and impressing said direct current voltage on the dynatron as a control grid oscillatingvoltagebecomestzeros I whereby the net bias falls to zero before $-;A, selfeoscillating .dynatron system compris ingrthe combination-with a; tube having? aicathode. cooperating,withia,controlgrid and at least two.

th r, elements, a resonant icircuit connected between: the pathode and the out?! One .of ,said i I elements-Jon tuning said oscillator overa frequency range, and means impressing on said I other elements steady potentials which are both positive with respect to said cathode and of q relative values which result in self-oscillation, of

, means actuated by the oscillating voltage to vary i the control grid bias automatically with changes in the amplitude of the oscillating voltage.

5. A self-oscillating dynatron as claimed in claim 4, wherein said bias-varying means inj cludes a rectifier.

f6. A dynatron oscillator comprising a dynatron tube having a cathode, a control grid and two other electrodes, aresonant circuit for tuning the dynatron over a frequency range, said tuned circuit being connected between the cathode and one of said other electrodes, a control grid circuit including a resistance, means impressing on said other electrodes steady potentials which are relative values producing dynatronoscillations, and means for developing across said resistance a direct current voltage that varies as a func- J tion of the amplitude of the oscillating voltage.

. 'T. A dynatron oscillator as set forth in claim 6, wherein said means includes a diode rectifier having an input circuit coupled to said resonant circuit, the said resistance being included in the output circuit of said diode rectifier. i

8. An oscillator comprising a tube having a cathode cooperating with a control grid and at least two other electrodes, a tuned oscillatory circuit between one of said other electrodes and the cathode, means impressing between the saidother electrodes and the cathode direct current potentials resulting in the generationof an oscillatory voltage across said tuned circuit, a resistance be tween control'grid and cathode, meansfor maintaining said controlgrid at the same oscillatory potential as said cathode, means including a rectifier for developing across said resistance a direct currentvoltage that varies automatically with .the amplitude of the oscillatory voltage, thereby to impress on the control grid a negative bias that becomes more negative with increases in the amplitude of the oscillatory voltage, and means I for reducing the bias'voltage to zero before the oscillatory voltage falls to zero.

9. The invention as set forth in claim 8, where- "in said last means comprises a source of direct current applying a fixed positive bias on the control grid. I

10. The invention as set forth in claim 8, wherein said last means comprises means for rendering said rectifier inoperative for peak os- .cillating voltages of less than a predetermined value. l

11. In a dynatron oscillator, the combination with a tube having acathode, control grid, a sec- 0nd grid and plate; of a tuned plate circuit, a

control grid circuit including a resistance, means for impressing on said second grid and plate steady potentials which are .both positive with respect to said cathode and of relative values resulting in the production of dynatron oscilla-. 'tions, and a diode having an input circuit cou-.

pled to said tuned plate circuit, said resistance comprising the output circuit of said diode.

)12Q'I 'II8II1V6IliJlOIl as set;;forth -.;inclaim 'l'lr, wherein. said. diodecomprises the 1 cathodeof said;

tube. nd an auxiliary plate element associated, therewith;

- 13; The inventionas set forth-tin ,claim ll, in; combination with means in said control gridg'ciri 'cuitfor modulating: the oscillating voltagey-de velopedacross-saidztunedplate circuit-,3. 1

14. A dynatron oscillator comprising a vacuum tube having cathode, control grid, screen grid, and plate elements, a resonant circuit coupled to said plate and cathode, a source of potential maintaining the screen grid at a higher positive potential than the plate with respect to the cathode, a resistance in circuit between said control grid and said cathode, means suppressing the development of oscillator frequency voltage between control grid and cathode, and means for impressing on the control grid a negative bias that becomes more negative with increases in the amplitude of the oscillatory voltages; said means including a rectifier having input means for impressing thereon a voltage which varies with the oscillatory voltage, and means for passing the output current of said rectifier through said resistance. i

15. In the operation of an oscillator of the type including a vacuum tube having a cathode, a plurality of cold electrodes, circuit elementscooperating with said cathode and cold electrodes to constitute an oscillatory network, a grid electrode, and means preventing the development of oscillatory voltages between said grid electrode and cathode, the method of controlling the amplitudeof oscillation which comprises rectifying oscillating energy developed in said network, and applying between the cathode and grid the voltage resulting from such rectification.

16. An oscillation generator comprising an electron discharge device having an electron emitting cathode, an anode, a screen grid, and a control grid, and means for causing the emission of secondary electrons from said anode, resonant means in circuit with the electrodes of said device for controlling the frequency of oscillations generated thereby, and means actuated in dependence upon the oscillatory output from said .device for applying a controlling bias potential to the control grid of said device whereby the amount of negative resistance exhibited by said device is automatically controlled in a direction to produce substantial constancy of output. 3

17. The method of stabilizing an electron discharge device oscillator whosecircuit includes an electron emitting cathode, an anode, a screen grid electrode, and an electron controlling member intermediate said cathode and screen grid, and means for causing an emission of secondary electrons from said anode which comprises rectifying the oscillations obtained from said anode in'excess of a predetermined value and utilizing the rectified oscillations for applying a bias potential to said electron controlling member thereby varying the number of primary electrons which may reach said anode with any given potential supplied thereto and the number of secondary electrons which will be efiectively emitted therefrom.

18. In combination, a negative resistance device comprising an electron discharge device having a cathode, anode, control grid, and screen grid electrode, resonant means in circuit withv the anode circuit of said device for controlling the frequency generated thereby, means for applying to the anode and screen electrodes of said tion of its anode-voltage-electron current to anode characteristic, the arrangement being such that the negative conductance of the anode circuit of said valve is greater in magnitude than the dynamic conductance of the external circuit, whereby said device operates as a dynatron oscillator, means for rectifying oscillatory current' derived from the output circuit of said valve and means for applying as bias potential components to the control grid of said device potentials derived from the rectified oscillatory current.

19. An oscillator as claimed in claim 18, and in which said rectifying means includes a diode.

PAUL 0. FARNHAM. 

